(v.) To lose
one's cool; become really pissed off. The idiom is in reference to a pressure
cap popping off, usually resulting in a
nasty burn or imminent explosion. Thus, the person who caused the pop off is about to get told or be destroyed, depending on the nature and severity of the inflammatory incident.
James: Vernie, your little wigga
child is uuuuugly.
Vernie: No you
di'int, heeeyll no, heyell no, heyell nah, heyell no, you said what, naaah, heyell no, heyell no, heeeyeeeell, no, etc.
{Vernie has popped off at James' comment}
-----------------------------------------
Boss: Dave, I know you're a family man, but I need you to come in Saturday... aaaaand Sunday, and stay late every night this week.
Dave: That's cool boss, I'm just gonna need your head in a
fucking drill press while I go to work on your
nuts with some bolt cutters and run an arc torch down your spine after I've nailed your feet to the floor with a remington power driver.
Boss: Okay Dave, no need to pop off now, I'll get
Clarence to do it.